Test and document src-expose on ec2 with docker-compose and startup

Created by: keegancsmith

This issue is targeted at testing out and documenting Sourcegraph with src-expose for https://app.hubspot.com/contacts/2762526/company/947819054/

• Happy with just a static binary that they can run alongside Sourcegraph docker containers.
• They do not care about having history
• Fine with writing the script and figuring out how to shard Perforce repo into smaller Git repos themselves
• Want us to provide an init script they can use so it reruns across restarts
• Keegan to follow-up with instructions for setting this up.